This invention relates to humidity sensing devices and especially to an improved electric hygrometer which measures over the full useful range up to 100 percent relative humidity.
Present humidity sensors based upon electrolytic conduction through a salt solution fail after exposure to 95 percent or greater humidity. The reason for this is lack of containment of the salt solution. One type has a bifilar winding on a rod that is coated with lithium chloride; the solution drips off the coated rod at these high humidities because the solution is tending toward infinite dilution and infinite volume in order to attain the vapor pressure of pure water. Another type consists of a porous membrane containing the salt in its pores and is described by the inventor in "Electric Hygrometer", Transactions of the AIEE, Vol. 77, Part I, Communication and Electronics, July 1958, pp. 302-305. This invention is an improvement over the foregoing.